1. Field of the Invention
In general, the present invention relates to emergency pressurization systems for aircraft that have pressurized cabins. The present invention also relates to aircraft systems that utilize secondary turbines to compress air, wherein the secondary turbines are driven by the bleed air from an aircraft engine.
2. Prior Art Description
Low flying, relatively slow aircraft do not require sophisticated environmental controls for inside the aircraft. The quality of the air within the aircraft can be adjusted simply by opening and closing vents or windows. However, many modern aircraft are designed to fly at high speeds and at high altitude. Such aircraft require pressurized cabins, where the pressure within the aircraft is artificially maintained. If an aircraft cabin is pressurized, fresh ambient air cannot simply be vented into the pressurized cabin. Rather, fresh air must be compressed to a pressure that matches that of the interior of the pressurized cabin, thereby enabling the fresh air to flow into the pressurized cabin.
Aircraft that are designed to fly at high altitudes typically have jet engines or turboprop engines. Pressurized air is created by such engines. By bleeding some air from the engine, a source of high temperature/high pressure air can be obtained. In early designs for aircraft environmental control systems, engine bleed air was directly used to feed air into a pressurized cabin. Such an environmental control system is exemplified by U.S. Pat. No. 3,537,510 to Rennenberg, entitled Pressure And Temperature Regulator For Aircraft Bleed Air System. However, engine bleed air is typically at a high pressure and at a high temperature. A sophisticated heat exchanger and pressure valve regulator configuration must therefore be used to condition the bleed air so it is at the correct temperature and pressure to be introduced into the cabin.
Aircraft are sophisticated machines. Like all machines, the components of an aircraft wear and are subject to eventual failure. Should a door seal, window seal, vent, or fuselage seam of an aircraft fail, the cabin of the aircraft may experience sudden decompression. If the aircraft is flying at high altitudes, there may not be enough oxygen in the ambient air to breathe. Furthermore, the sudden change in pressure can cause unconsciousness in less than sixty seconds.
In many aircraft, emergency oxygen is available in the event of cabin decompression. The oxygen enables the pilot to breathe so that the pilot can make an emergency descent to an altitude of below 12,500 feet. Once at such an altitude, ambient pressure and oxygen levels are sufficient to maintain consciousness. However, an aircraft may not have the ability to rapidly descend to such an altitude. If an aircraft is flying over mountains or a storm, such a decrease in altitude may not be possible. Furthermore, if the aircraft is flying over an ocean, the decrease in engine efficiencies created by the descent in altitude may cause the aircraft to lack the fuel needed to reach its destination.
In order to avoid these problems, some aircraft contain emergency pressurization systems. The emergency pressurization systems automatically pump pressurized air into the aircraft cabin. Hopefully, the emergency pressurization system can add air to the cabin faster than pressurized air is leaking from the cabin and the cabin pressure can be maintained.
In the prior art, emergency pressurization systems typically direct pressurized engine bleed air directly into the aircraft cabin. Engine bleed air is very hot. The engine bleed air also contains engine fumes, water vapor and other contaminants. Consequently, a pilot must still find a way to quickly descend to a safe altitude before the pilot and passengers are overcome by the heat and the contaminated air.
A need therefore exists for an improved emergency pressurization system for an aircraft that can supply pressurized air into the aircraft cabin without ever directing engine bleed air into the cabin. This need is met by the present invention as described and claimed below.